1. Field of the Invention
This invention pertains in general to systems and methods of providing voice communications for a radio network, and more particularly, to systems and methods of providing Voice-over-Internet-Protocol service for a radio network between a wireless communication device and an end terminal in a packet data network.
2. Description of the Related Art
Global System for Mobile communications (“GSM”) has become a popular technology for digital mobile phones and a predominant system for mobile communications in Europe and numerous other countries around the world. GSM, a circuit-switched system, however, is not designed for data communications. As a result, traditional GSM system was not able to provide satisfactory services for data communications, which require high degree of accessibility, high data communication rate, and low cost. General Packet Radio Service (“GPRS”) was proposed to resolve the problems of providing data communications in a GSM network. The GPRS operates to provide data packet exchange services under the existing GSM networks and systems. The core network of the GPRS has become part of the second generation of the Time-Division-Multiple-Access (“TDMA”) cellular system, or the so-called Interim Standard-136 (“IS-136”) TDMA system. IS-136 is a North American digital mobile telephony standard based on TDMA technology. It is a TDMA specification that is used to create in a fully digital second generation system and is backward compatible with analog Advanced Mobile Phone System (“AMPS”). It is expected that the GPRS will be further developed as the core network of the third-generation mobile phone system.
The demand of providing voice communications over the Internet, the so-called Voice-over-Internet-Protocol (“VoIP”) service, has been greatly increased in the last several years. Gardell et al. described, in U.S. Pat. No. 6,128,304, a method and apparatus for providing traditional telecommunications services capabilities in a packet-based computer network. Their invention is directed to the application of such services in an H.323-based system but did not apply to wireless systems.
Combining VoIP service with mobile phone systems is one of the important goals of current development efforts. Most recent developments on VoIP service involved providing the service in Internet-based networks, or between an end terminal in the Internet and a traditional telephone terminal. Other GPRS developments focused on the control and efficiency of data packet transmissions. Dahlin et al. proposed, in U.S. Pat. No. 6,122,263, a scheme for providing Internet access for cellular networks, which receives and analyzes packets from a packet-switched fixed network. Their invention enabled routing of wideband traffic from a packet-switched fixed network over a radio interface to a mobile terminal, but did not provide VoIP service for a GPRS network.
FIG. 1 is a block diagram illustrating the main structure of a known GPRS network 10. GPRS network 10 includes several elements of a traditional GSM network, including a Base Transceiver Station (“BTS”) 12, a Base Station Controller (“BSC”) 14, a Mobile Switching Center (“MSC”) 16, a Home Location Register (“HLR”) 18, and a Visitor Location Register (“VLR”) 20. In addition to traditional GSM network elements, GPRS network 10 further includes a Serving GPRS Support Node (“SGSN”) 22 and a Gateway GPRS Support Node (“GGSN”) 24. A wireless communication device 30, such as a GSM mobile phone, communicates with GPRS network 10 through BTS 12. SGSN 22 and GGSN 24, through the channeling of other devices, transmits data packets between the wireless communication device 30 and a data network 32, such as a Public Switched Data Network (“PSDN”), or namely, the Internet.
BSC 14 includes a base station Packet Control Unit (“PCU”) 14b in order to communicate with SGSN 22. As a result, BSC 14 directs circuit-switched voice signals to MSC 16 and directs packet-switched data to SGSN 22 through the base station PCU 14b. MSC 16 then directs voice signals of ordinary phone calls to a Publicly Switched Telephone Network (“PSTN”). Traditionally, one BSC 14 can communicate with only one SGSN 22. GGSN 24, which communicates with SGSN 22, communicates with external data network 32. SGSN 22 and GGSN 24 are responsible for communicating with HLR 18 and VLR 20 in order to locate a wireless communication device, such as a mobile phone.
Therefore, wireless communication device 30 communicates with the Internet in data packet form through the operation of BTS 12, BSC 14, SGSN 22, and GGSN 24. A traditional GPRS network does not support VoIP services because wireless communication device 30 has no capability of processing H.323 packets. Further, no specific schemes are designed to register mobile phones to data network 32 and to allow mobile phones to initiate a phone call to or receive a phone call from an end terminal in data network 32.
To resolve the problem, one of the proposed specifications and studies for third generation mobile systems, 3G TR 21.978, provides a VoIP scheme for a GPRS network. 3G TR 21.978 is a document developed within the third-generation partnership project. The document contains a feasibility report of the proposed VoIP scheme that enables VoIP calls between third-generation (3G) terminals or between a 3G terminal and legacy network terminal, such as second-generation (2G) mobile, Integrated Service Digital Network (“ISDN”) or PSTN. The proposed scheme implements an “in-band signaling” concept that transmits signals and voice information with the same Packet-Data-Protocol (“PDP”) concept. The scheme requires deactivation of a PDP context previously activated after a mobile phone completes a registration procedure to a H.323 network. Therefore, the mobile phone has to reactivate the PDP context each time a user makes or receives a call. The time needed for establishing a phone conversation channel is increased by the repetition of deactivation and reactivation processes. Further, the scheme proposed in 3G TR 21.978 requires modification of a standard H.323 interface, such as a H.323 gatekeeper, in order to implement the proposed scheme. The required modification limits the application of the proposed scheme.